﻿<p>An <em>IfcCardinalPointReference</em> is an index reference to
significant points of a section profile. This index is used to
describe the spatial relationship between the section of a member
and a reference axis of the same member.</p>

<blockquote class="history">
HISTORY  New Type in IFC4.
</blockquote>

<p>Indexes 1...9 refer to points at the bounding box of a
profile. Indexes 10...19 refer to points defined by geometric
centroid (usually centre of gravity) and shear centre, and their
combinations with bounding box coordinates. In particular, the
following index values are specified in this specification:</p>
<ol>
<li>bottom left</li>
<li>bottom centre</li>
<li>bottom right</li>
<li>mid-depth left</li>
<li>mid-depth centre</li>
<li>mid-depth right</li>
<li>top left</li>
<li>top centre</li>
<li>top right</li>
<li>geometric centroid</li>
<li>bottom in line with the geometric centroid</li>
<li>left in line with the geometric centroid</li>
<li>right in line with the geometric centroid</li>
<li>top in line with the geometric centroid</li>
<li>shear centre</li>
<li>bottom in line with the shear centre</li>
<li>left in line with the shear centre</li>
<li>right in line with the shear centre</li>
<li>top in line with the shear centre</li>
</ol>
<p>Other index values are possible but outside the scope of this
specification.</p>

<p>Figure 3 illustrates cardinal point values.</p>
<table>
<tr><td><img src="../../../figures/ifccardinalpointreference-01.png" alt="arbitrary profile with cardinal points" border="0" width="676"height="264"></td></tr>
<tr><td><p class="figure">Figure 3 &mdash; Cardinal point values</p></td></tr>
</table>

<p>Figure 4 illustrates an example extrusion shape with arbitrary profile (<em>IfcArbitraryClosedProfileDef</em>), aligned "mid-depth right" on the member axis. The line of sight follows the extrusion direction Z which points into the drawing plane of above illustration. Hence, "left" is in the positive X direction of the <em>IfcProfileDef</em>. "Top" is in the positive Y direction of the <em>IfcProfileDef</em>.</p>

<table>
<tr><td><img src="../../../figures/ifccardinalpointreference-02.png" alt="extrusion shape with arbitrary profile and alignment" border="0" width="357" height="236"></td></tr>
<tr><td><p class="figure">Figure 4 &mdash; Cardinal point extrusion</p></td></tr>
</table>